How a fine spray of water can help automakers build cleaner engines

The first production BMW fitted with a water-injection system was the M4 GTS, a limited-edition model with a six-digit price tag. The GTS sold out almost immediately, but the fuel-saving technology is set to trickle down to more affordable cars in the coming years.

German components manufacturer Bosch is working on bringing water injection to the masses. And while the system primarily helped the M4 GTS’ turbocharged 3.0-liter straight-six develop more power, Bosch engineers explained that it’s capable of boosting efficiency by up to 13 percent while reducing CO2 emissions by 4 percent.

Water injection can be fitted to all types of cars, though Bosch project manager Fabiana Piazza told British magazine Autocar that the system works best when it equips an engine with an output of over 107 horsepower per liter of displacement.

In laymen’s terms, a water injection system injects a fine, precisely-measured spray of water into the intake manifold. As it evaporates, the water extracts energy from its surroundings and lowers the temperature of the intake air by up to 80 degrees F. The process boosts gas mileage, lowers emissions and improves both torque and power.

The system isn’t as complex as it might initially sound. It’s essentially made up of a 1.3-gallon frost-proof tank located in the trunk, a pump, valves and a host of sensors. The components are maintenance-free but the tank needs to be topped up occasionally. The engine still runs if the tank is empty, though it generates less power and it emits more CO2.

Bosch expects the first series-produced cars fitted with water injection will arrive in 2019.

“We are in contact with major automotive makers already, but we can’t talk about them in more detail at this stage. We can say that we expect the system to make mass production from 2019,” project head Martin Frohnmaier revealed.

BMW co-developed the system, so it’s reasonable to assume that it will be one of the first brands to adopt the technology. However, Bosch is free to license it out to anyone willing to pay for it. If BMW moves forward with water injection, expect rivals Mercedes-Benz and Audi to follow suit shortly after.